1. Field of the Invention
The invention relates to a blue photosensitive resin composition for a color filter and a liquid crystal display device formed therefrom; particularly, to a blue photosensitive resin composition for a color filter having good developing-resistance, good ageing stability of sensitivity and good contrast.
2. Description of the Related Art
Along with advancing technology and broadening applications, large-sized liquid crystal display devices with high color reproduction, such as liquid crystal display televisions, are being actively developed. Generally, NTSC color reproduction of desktop liquid crystal display devices ranges roughly from 50 percent to 60 percent while NTSC color reproduction of the liquid crystal television ranges roughly from 60 percent to 75 percent. Therefore, mere application of the components for the desktop liquid crystal display device, such as a liquid crystal display element and a backlight unit (for example, cold cathode fluorescent lamp (CCFL)), to the liquid crystal display television is not able to satisfy the color reproduction requirement for the liquid crystal display television.
When the backlight unit of the desktop liquid crystal display is used for the liquid crystal display television, a color filter must have a thicker blue filter segment or a denser blue pigment to satisfy the requirement of the color reproduction for the liquid crystal display television, which, however, may lead to drastic decrease in light permeability of the blue color filter segment.
JP-H09-095638 discloses a blue photosensitive resin composition for forming a color filter which is composed of an alpha-copper phthalocyanine blue pigment, an epsilon-copper phthalocyanine blue pigment, a photosensitive resin, a photoinitiator, and a solvent. Furthermore, JP-H09-197663 also discloses a blue photosensitive resin composition for forming a color filter which is composed of a copper phthalocyanine blue pigment, an indanthrone blue pigment, a photosensitive resin, a photoinitiator, and a solvent. These two blue photosensitive resin compositions can solve the abovementioned light permeability issues.
The blue photosensitive resin compositions disclosed in the above-mentioned patents both use different blue pigments to improve the light permeability. However, the increase of the concentration of the pigments would lead to the decrease of the contrast of the color filter comprising the blue photosensitive resin compositions because light scattering occurring due to the particle diameter of the pigments. Therefore, Japanese Patent Publication No. 2006-079012 discloses a pyrazole squarylium dye that only absorbs light to present color and a blue pigment 15:6 to increase the contrast of the color filter. However, the ageing stability and developing-resistance are both not satisfactory.
Furthermore, in order to meet the modern requirement of color saturation, the concentration of the pigment must be raised and a high-dose photoinitiator must be incorporated. However, when mixing the high-concentration pigment and a common photoinitiator, the ageing stability is poor. In addition, using the high-concentration pigment, the ratio of the pigment of the photosensitive resin composition is also high and the used amounts of an alkali-soluble resin and photosensitive monomer decrease. Such phenomenon leads the decrease of the degree of cross-linking after exposure and poor develop-resistance.
Therefore, improving developing-resistance, ageing stability of sensitivity and contrast of the liquid crystal display device to meet the modern requirements is a target remained to be achieved in the technical field of the present invention.